1. Field of the Invention
The invention relates to a method and the apparatus for automatic multi-run welding of a joint formed by two joint surfaces, in which method the contour of the joint is scanned by a sensor which emits signals corresponding to the shape of the joint, which signals, after evaluation, control the deposition of the weld beads by means of a continuously fed electrode which is movable in at least three directions, is directed towards a welding point in the joint by means of an arc weld head and is moved relatively along the joint.
In welding, account must be taken of the variations in the cross-sectional area of the weld joint along the joint. The cross-sectional area is determined, on the one hand, by the contour of the joint and, on the other hand, by a line which connects the two joint edges. The cross-section of the joint often differs from the ideal shape, for example a V-shape, U-shape etc. In the case of long joints, the width of the joint usually varies, and the joint edges are often offset relative to each other. The cross-sectional area along the joint therefore alters continuously on account of the geometric imperfections of the joint, which are essentially caused by production-engineering in the joint preparation. In automatic welding in particular, it must be possible for these variations in the joint cross-section along the joint to be recorded, so that the beads can be deposited with a chosen amount of welding material per unit of length, which finally results in a joint which is even and filled to the same level. In manual or semi-automatic welding, the welder can vary the welding parameters, for example the welding speed, in order to compensate for irregularities in the weld joint. In the case of automatic welding, such adaption of the welding to these variations must be effected entirely automatically.
2. Description of the prior art
EP-B1-12,962 describes a procedure of the type mentioned in the introduction. On the basis of the actual joint width scanned by a sensor, the number of weld beads to be deposited alongside each other is selected automatically, and the transition from one bead to the next is carried out in accordance with a specific procedure. However, during the welding, no account is taken of the variations in the cross-section of the joint, which cross-section is affected not only by the joint width, but also to a significant extent by the joint offset.
In another proposal, U.S. Pat. No. 4,608,481, the joint is filled by means of an oscillating movement of an electrode, and the shape of the joint is scanned at the same time by means of, for example, measuring the arc voltage during the oscillating movement at certain relative positions of the welding burner in relation to the workpiece. This procedure requires additional arrangements for the oscillating movement and separate control equipment for the movement.